【作者】 鄢全树；

【导师】 钟增球；

【作者基本信息】 中国地质大学 ， 矿物学、岩石学、矿床学， 2004， 硕士

【摘要】 大别造山带为中央造山带的一部分，其东南缘被郯—庐断裂所切割，可与苏鲁造山带相连，直至朝鲜的临津江变质带；西越过南襄盆地可与秦岭造山带相望。大别造山带的整体构造样式类似于北美西部的科迪勒拉型变质核杂岩，其中的超高压岩石构造单元位于核部杂岩单元与高压单元之间，超高压变质岩形成的动力学背景目前有了趋于一致的认识，即印支期印支期中朝克拉通与扬子克拉通会聚和碰撞的产物。 本文从野外露头分析、岩相学、岩石化学、变质矿物特征等方面探讨了碧溪岭和四道河这两个剖面的岩石组合及其超高压板片在折返期间演化规律。得出了以下主要认识： （1） 两剖面的岩石组合都包括以下三大类：①榴辉岩类，其中包括榴辉岩、榴闪岩以及斜长角闪岩，在大的榴辉岩透镜体可以清晰的辨认出从榴辉岩→榴闪岩→斜长角闪岩的渐变过渡关系；②片麻岩，为榴辉岩的直接围岩；③面理化（含榴）花岗岩，与片麻岩的界线模糊，或为榴辉岩的直接围岩。三大类岩石的界线都很模糊，显示渐变过渡的特点。以上三类岩石共同组成了超高压单元。 （2） 榴辉岩类岩石往片麻岩及面理化（含榴）花岗岩转变的过程中，根据岩石中的矿物共生组合可以识别出以下三期变质作用：①峰期超高压变质作用（石榴石+绿辉石+金红石±柯石英（或其假象））、②角闪岩相退变质作用（角闪石+斜长石组成的后成合晶）以及③绿帘角闪岩相变质作用（绿帘石+角闪石±黑云母+少量的钠长石等组成的石榴石斑晶假象）。在此演变过程中，石榴石岩相学特征如下，由斑晶完好逐渐转变为细粒呈“孤岛状”的石榴石与退变矿物组成的斑晶假象，直至最后在局部出现完全被退变矿物所取代的斑晶假象。 （3） 在主量元素方面，在榴辉岩类岩石向片麻岩及面理化（含榴）花岗岩演变的过程中，主量元素存在系统的成分变异，随SiO₂含量的增高，TiO₂、Al₂O₃、MgO、CaO、FeO、P₂O₅等呈现一定的负相关关系，而K₂O、Na₂O呈现正相关关系。结合国外实验岩石学资料，表明这种同源演化的可行性。在微量和稀土元素方面，两剖面各岩石类型的微量元素存在相似性，都呈现了一定的壳源特点；在稀土配分曲线图上，从榴辉岩往片麻岩及面理化（含榴）花岗岩演变的过程中，可以清晰地看出轻稀土逐步富集，曲线形态由左倾转为右倾。 （4） 变质矿物特征方面，由具三端元组分的榴辉岩中的石榴石演变为片麻岩及面理化（含榴）花岗岩中的四端元组分的石榴石，石榴石端元组分含量发生了明显的变化，锰铝榴石的含量提高显著。四道河剖面石榴石端元组分含量变化如下：Pyr=15％-29％，Gro=17％-40％，Alm+Spe=45％-54％（榴辉岩）；Pyr=8％-10％，Gro=30％-43％，Alm=44％-56％，Spe=3-6％（片麻岩）；Pyr=3％-16％，Gro=31％-36％，Alm=37％-49％，Spe=3-24％（面理化（含榴）花岗岩）。碧溪岭剖面石榴石端元组分含量变化如下：Pyr=20％-22％，Gro=20％-25％，Alm+Spe=55％-58％；Pyr=12％-15％，Gro=34％-40％，Alm=44％-51％，Spe=1-2％；Pyr＜1％，更多还原

【Abstract】 The Qinling-Dabie collision zone between the Sino-Korean and Yangtze cratons in central China extends -2000 km from the western Qinling Mountains through the Tongbai to the Dabie Mountains. Its eastern extension has displaced northward by the sinistral Tan-Lu fault to the Sulu region. Dabie collisional orogenic belt is an important portion of the Qinling-Dabie collision zone, and it displays typical feature of a Cordilleran-type metamorphic core complex. It is commonly accepted that the UHP terrane was formed in Triassic by the continental collision between the Sino-Korean and Yangtze cratons.Some conclusions about the rock associations and its evolution of Bixiling and Sidaohe areas in the UHP metamorphic terrane are proposed as follows.(1) The UHP metamorphic terrane are composed mainly of crustal and mantle-derived rocks that have undergone UHP metamorphism, retrograded UHP metamorphic rocks, as well as gneisses and foliated garnet-bearing granite. Firstly is the ecologitic rocks including eclogite, eclogitic amphibolite and amphibolite (symplectite of plagioclase+amphibole). In some localities where large eclogite bodies occur, there is a gradual transition of eclogite→eclogitic amphibolite →amphibolite. Secondly is the gneiss, which is straight country rock of the eclogitic rocks, there is a gradual transition between eclogite and gneiss. Thirdly is the foliated granite, there is a gradual transition between gneiss and foliated granite. In a word, there is a gradual transition of eclogite→gneiss→foliated granite.(2) During the process of evolution from eclogitic rocks to gneiss and foliated granites, the most obvious characteristic showing on garnet mineral is that transition from integrated garnet phenocryst to small particle, the "isolated island" garnet phenocryst, which composed of garnet phenocryst pseudomorphs and retrograde minerals. The typical equilibrium parageneses of the minerals in rocks are distinguished into three metamorphic stages: (1) Grt + Omp + Rut ±Coe (or pseudomorphs ) (Peak metamorphism, only in Bixiling area); (2) Hbl + Pl (which forms symplectite on rim of garnet and omphacite) (amphibolite retrograde metamorphism); and (3) Epi + Hbl ± Bi ± garnet + sodium feldspar (which forms garnet phenocryst pseudomorphs) (epidote-blueschist retrograde metamorphism).(3) During the evolution process from eclogitic rocks to gneiss and foliated granites, with the increase of the SiO2 content, the contents of TiO2, A12O3, MgO, CaO, FeO and P2O5 decrease accordingly, and the contents of K2O and Na2O increase accordingly. Combined to datum of experimental petrology, it exists systematic compositional variation among these three type rocks. Trace elements show the characteristics of crustal source. In REE patterns, from eclogite to gneiss and foliated garnet granites, LREEs show gradual enrichment and the curve of REE patterns change from left-trend to right-trend.(4) During the evolution process from eclogites to gneiss and foliated ganites, Garnet composition have been changed remarkably, especially in contents of spessartine. The contents of更多还原